1. Field of the Invention
This invention relates in general to wireless cellular communication devices capable of multiple-input, multiple-output (MIMO) communication and/or receive diversity and, more particularly, to utilizing the transmit local oscillator (LO) to drive a receiver when the transmitter in not in use.
2. Description of the Related Art
A wireless communication device (WCD), such as a cellular telephone, for instance, is required to utilize multiple radio access technologies and multiple frequency bands when performing measurement and synchronization on communication cells. This occurs in the transition from switch-on to camp-on when locating the best cell on the best network and is maintained in Idle mode and in Dedicated mode. Although the WCD must cycle through the multiple radio access technologies and multiple bands, the operator (and end-user) desires a fast reaction time as the radio conditions change.
In a mobility context where the user and/or environment are moving, abrupt shadowing effects are common, e.g., when a device moves around a corner or cars move around a device. This often leads to repeated interruptions in communication. However, users demand mobile voice communication hardware and techniques that will provide seamless handovers when one link breaks. To ensure a seamless handover, the WCD must cycle through the multiple radio access technologies and multiple bands to perform measurements and synchronize on different communication cells. This is a lime and resource limited process. Unfortunately, some radio access technologies such as WLAN or WAN, do not intrinsically support mobility and soft handoffs. Due to these technology limitations, prior art equipment can degrade the user experience.
The reaction time and performance of cell measurement and synchronization can be improved with the operation of two receivers simultaneously to perform concurrent multiple band searches, measurements, and synchronization. Several wireless standards, such as the 802.11n standard defined by the Institute of Electrical and Electronics Engineers (IEEE), now require two or more receiver channels on the modem either for receive diversity, interference cancellation, or two-port Multiple-Input, Multiple-Output (MIMO). However, these receivers can not always be operated independently due to performance gains associated with receive diversity, interference cancellation, or two-port MIMO operation. A method is needed to identify opportunities when both receivers can be operated independently. In addition, the receivers typically share a single Local Oscillator (LO) and the receiver channels are, therefore, tuned to the same Radio Frequency (RF) center frequencies and channel bandwidths. The addition of a second receive LO to the WCD for the purpose of measuring other frequencies is not desirable from a complexity and cost standpoint.
Therefore a need exists to overcome the problems associated with the prior art as discussed above.